Measuring the filtration performance of breathing system filters using sodium chloride particles.

The filtration performance of 33 breathing system filters (nine pleated hydrophobic and 24 electrostatic filters) was measured using sodium chloride particles. The particles had a size distribution with a count median diameter of 0.07 microm and a geometric standard deviation not exceeding 1.83. The geometric mean penetration values ranged from 0.002 to 0.67% for the nine pleated hydrophobic filters and from 0.25 to 35% for the 24 electrostatic filters (p < 0.0001 for the difference between the two filter types). The filtration performance obtained when filters are challenged with either sodium chloride particles or microbes is compared and discussed.